Electroluminescent lamps typically provide approximately 30 foot-lamberts of illumination and are thus suitable for various low-intensity illumination applications, such as decorative lighting, egress lighting, cockpit and dashboard display panels, and membrane switches. They have also been used as backlighting sources for liquid crystal display (LCD) devices. However, most LCD applications, including black/white and color LCD displays and high definition displays, require greater backlighting illumination than electroluminescent lamps can provide. Furthermore, most electroluminescent lamps have poor maintenance characteristics: they typically degrade to about half their initial brightness within 2000 hours of operation.
Zinc sulfide electroluminescent phosphors and methods of making them are described in U.S. Pat. Nos. 2,807,587 to Butler et al., 3,031,415 to Morrison et al., 3,031,416 to Morrison et al., 3,152,995 to Strock, 3,154,712 to Payne, 3,222,214 to Lagos et al., 3,657,142 to Poss, and 4,859,361 to Reilly et al., all of which are assigned to the assignee of the instant invention. However, none of these electroluminescent zinc sulfide phosphors are sufficiently bright for use in most LCD backlighting applications or high definition display devices.
It would be an advantage in the art to provide a copper-activated zinc sulfide electroluminescent phosphor having improved luminance and maintenance for use in LCD and high definition display devices, and a method of making the phosphor.